The present inventor relates to the field of noise and vibration reduction. More particularly, the invention relates to an apparatus and related method for actively reducing the noise and vibration produced by a machine through electroactive waveform control of the drive current.
In many cases, the operation of a machine powered by an electrical motor, such as found in a fan, creates undesirable noise. The noise generated by a fan typically includes both mechanical vibrations and aerodynamic vibrations, or sound. Mechanical vibrations can be caused, for example, when the fan is not properly balanced. The rotation of the imbalanced fan results in mechanical vibrations in the structure that supports the fan.
Aerodynamic vibrations, or sound, are typically generated when the fan blade interacts with unsteady airflow. Unsteady airflow can exist around a stator or any other fan support structure. The interaction of the fan blades with the unsteady airflow causes aerodynamic vibrations to radiate away from the fan and into the surrounding environment. These aerodynamic vibrations may either impinge on the fan structure thereby creating vibrations or continue to propagate as sound.
There are many circumstances where it is desirable to reduce or eliminate the noise generated by a fan. This is particularly apparent when the fan is used as a cooling device within an electrical device installed on board a submarine. Any structure-borne or air-bome noise generated by the fan will eventually propagate to the outer edge of the submarine where it will be radiated into the surrounding water. Obviously, any additional noise generated by the submarine increases the chances of the submarine being detected. Thus, eliminating the noise generated by the fans in the electrical devices carried on board the submarine will decrease the cumulative noise generated by the submarine, thereby decreasing the likelihood that the submarine will be detected.
In other circumstances, the noise generated by electric fans creates an annoyance or disturbance to those near the fan. For example, a noisy fan within an overhead projector can be a distraction when the overhead projector is in use. The operation of other machines, such as HVAC system components, pumps, and propellers, also generate annoying or disturbing noise.
In light of the foregoing there is a need for a device and method capable of reducing the vibrations and sound generated by a machine.